Changes in XMBF 1.80:
---------------------

- added new fit models (see the user manual for details):
  "multi_exp_nonsym_mat_model",
  "multi_exp_expE_nonsym_mat_model",
  "multi_alt_exp_nonsym_mat_model",
  "multi_alt_exp_expE_nonsym_mat_model",
  "multi_exp_2var_model",
  "multi_exp_expE_2var_model",
  "threept_constant_model",
  "threept_constant_sqr_model"

- added the option "bootstrap_normalization" in "fit_settings".
If set to "true", the normalization of the data correlation matrix is changed
(see the user manual for details)

- XMBF now checks the uniqueness of the parameter names within each individual model

- fixed the following minor bug: "threept_multi_exp_expE_model" and "threept_multi_alt_exp_expE_model" were
returning an incorrect function string (did not affect the fitting at all, just the printout).